Role of muscle mass and mode of contraction in circulatory responses to exercise.

The roles of the mode of contraction (i.e., dynamic or static) and the active muscle mass as determinants of the cardiovascular responses to exercise were studied. Six healthy men performed static handgrip (SHG), dynamic handgrip (DHG), static two-knee extension (SKE), and dynamic two-knee extension (DKE) to local muscular fatigue in approximately 6 min. Increases in mean arterial pressure were similar for each mode of contraction, 29 +/- 5 and 30 +/- 3 mmHg in SHG and DHG and 56 +/- 2 and 48 +/- 2 mmHg in SKE and DKE (P greater than 0.05) but larger for KE than HG (P less than 0.001). Cardiac output increased more for dynamic than for static exercise and for each mode more for KE than HG (P less than 0.001). Systemic resistance was lower for dynamic than static exercise and fell from resting levels by approximately 1/3 during DKE. The magnitude of the pressor response was related to the active muscle mass but independent of the contraction mode. However, the mode of contraction affected the circulatory changes contributing to the pressor response. Equalization of the pressor responses was achieved by proportionately larger increases in cardiac output during dynamic exercise.